The organization of Moloney murine leukemia virus (M-MuLV) DNA sequences with the host cell genome will be studied at two levels: the arrangement of inserted viral DNA sequences in host cell DNA both in productively infected and transformed cells, and the localization of inserted viral DNA sequences in chromatin fractions separated on the basis of transcriptional activity. Experiments are proposed to map inserted viral DNA sequences by restriction endonuclease cleavage, and to clone, via recombinant DNA technology, inserted viral DNA sequences and their flanking host cell sequences. In additional, using cell lines carrying a single insertion of M-MuLV in a transcriptionally repressed but inducible state, chromatin fractionation procedures will be developed to separate active from inactive chromatin fractions.